This invention relates to an image fixing apparatus for fixing an image transferred onto a continuous form and, more particularly, to a mechanism for preventing meandering of the continuous form in the image fixing apparatus.
Conventionally, there is known an image recording device utilizing a so-called electrophotographic system in which a surface of a photoconductive drum, for example, is exposed to form a latent image on the drum surface, toner is then applied to the latent image to develop the image, and the developed image is transferred onto a recording sheet material and is fixed by a fixing apparatus. Such image recording device is chiefly employed in a copying machine. In general, cut sheets are used as the recording sheet material, and a heat-roll fixing system is utilized wherein the toner is fixed by heat as well as pressure. In addition, a pressure-fixing system has recently been developed, which is low in electric power consumption and which does not require an amount of time for preheating the heat rolls.
In recent years, the image recording device utilizing the electrophotographic system has also been employed in a printer or the like which prints out the output from a computer. In such image recording device, it has been desired to use, as the recording material, a continuous recording form identical with that used in a conventional line-printer.
The continuous recording form identical with the conventional one is a folded continuous recording form (hereinafter referred to simply as "continuous form") called a fan-folded form which has formed therein sprocket holes. Perforation is provided at each of the folded sections to enable sheet sections to easily be severed from each other.
In the above heat-roll fixing system or the pressure-fixing system, a continuous form having carried thereon unfixed toner image is clamped between a pair of rotating fixing rolls and is heat-pressurized or pressurized thereby, so that the toner image is squeezed onto the continuous form and is fixed thereonto. Usually, the continuous form is driven to travel by rotation of the fixing rolls.
When the above fixing systems are applied to the continuous form, the following fatal problem might arise. That is, the continuous form clamped between the fixing rolls would skew or meander because of various factors such as poor initial biting of the continuous form into the nip between the fixing rolls, unevenness or nonuniformity in thickness of the continuous form, elongation of the continuous form due to absorption of moisture, and the like. If such skewing or meandering occurs, the biting position of the continuous form with respect to the fixing rolls consecutively varies laterally, so that the side edge of the continuous form finally reaches the lateral end of the nip between the fixing rolls. This causes creases in the continuous form, resulting in defective fixing of the image and in defective transportation of the continuous form.
Such skewing or meandering of the continuous form does not occur in the case of cut sheets, because the cut sheets are limited in length, i.e., are relatively short in length.